(1) Field of the Invention
This invention relates to an adhesive fluorocarbon polymer shaped article.
(2) Description of Prior Art
It has been well known that fluorocarbon polymers have superior characteristics such as heat resistance, chemical resistance, transparency, ultraviolet ray deterioration resistance, humidity resistance, electric characteristics and so on as compared with other polymer materials. But it also has been said that they are defective because a shaped article of fluorocarbon polymer has only a inferior adhesive properties. Thus it has been desired to improve the adhesive properties of fluorocarbon polymer shaped articles, especially their heat-sealable adhesive properties. In this connection, the following proposals have been made for reforming the surface of a fluorocarbon polymer shaped article to improve adhesive properties.
(1) E. R. Nelson et al method for treating polytetrafluoroethylene with sodium naphthalene solutions (Ind. Eng. Chem., 50 329, 1958). This method has most commonly been used for improving adhesive properties of polytetrafluoroethylene polymers, but it lowers adhesive strength day by day, and exposure to ultraviolet rays reduces adhesive strength and causes color changes. Furthermore the method is not capable of giving the polytetrafluoroethylene sufficient heat-sealing properties.
(2) T. Moriuchi et al (proceedings of the 7th Int'l Vac. Cong. & 3rd Int'l Conf. Solid Surfaces; 1977) in this method for improving the adhesive property of polytetrafluoroethylene, characteristic cone-like structures are developed on the polymer surface by sputter etching, and thereby polytetrafluoroethylene is made adhesive with epoxy adhesives. Polytetrafluoroethylene treated by this method, however, is not suitable for acrylic adhesives. Furthermore the method is defective in that the characteristic cone-like structure is readily deteriorated by friction to cause the loss of adhesive properties.
(3) In J. Richard Hall et al method, J. Appl. Polym. Sci., 16, 1465, 1972). various kinds of polymers including fluorinated ethylene-propylene copolymers are treated with a low-temperature plasma of He or O.sub.2 gas at a discharge output of 50 W for one to 50 minutes, and the adhesive strength of the treated polymer with aluminum plate by an epoxy adhesive is examined. According to the result of their experiment, fluorinated ethylene-propylene copolymers are not considerably improved in adhesive properties through low-temperature plasma treatment, though a variety of other polymers are contrary. In experiments of the present inventors the same results have been obtained and it was confirmed that the products have no heat sealing properties.
(4) U.S. Pat. No. 3,627,624 discloses a method for improving fluorinated ethylene-propylene copolymers in adhesive properties to polyimide film through treatment with corona discharge in an atmosphere containing acetone vapor at atmospheric pressure. The products of this method, however, are faulty in that their adhesive property is lowered at high temperature, under high humidity or on exposure to ultraviolet rays. Furthermore the corona discharge treatment tends to cause problems in uniformity of quality.
The methods (1), (3) and (4) are intended to improve fluorocarbon polymers in adhesive properties by changing the chemical composition at their surfaces, and method (2) by changing their configuration at the surface. All of them, however, have such defects and disadvantages as stated above.